The present invention relates generally to integrated circuit memory devices, and more specifically to block decoded redundant master wordlines of integrated circuit memory devices.
In a variety of integrated circuit memory devices, such as static random access memories (SPAMs), including large density SPAMs (1 Meg, 4 Meg, 16 Meg, etc.), synchronous as well as asynchronous memory devices, and even slower commodity memory devices, it is often necessary to replace local wordlines which are faulty with functional redundant local wordlines. In the art, this is often accomplished by replacing all the local wordlines associated with a global wordline of a memory device, even those which are not faulty, with a redundant global wordline and its associated redundant local wordlines. Needless to .say, this way of replacing a faulty local wordline is very inefficient.
Referring to FIG. 1, a block structure 10 of a 1 Meg SRAM memory device is shown. The 1 Meg SRAM has a redundant global wordline 12 which spans across sixteen blocks, as shown, and controls two local wordlines in each block. For instance, Block0 has a local wordline pair comprised of local wordlines LWL00 16 and LWL10 24; Block1 as a local wordline pair comprised of local wordlines LWL01 18 and LWL11 26; Block2 has a local wordline pair comprised of local wordlines LWL02 20 and LWL12 28; finally, Block15 has a local wordline pair comprised of local wordlines LWL015 22 and LWL115 30, as shown. Local wordline decoder 14 decodes a block and its associated even/odd local wordline.
When a bad local wordline is found, all the local wordlines associated with the global wordline, across all sixteen blocks, are replaced by redundant global wordline 12. As is well known in the art, a local wordline is analogous to a row within a block of the memory. Thus, thirty-two local wordlines are replaced by redundant global wordline 12. Since there are 128 cells per local wordline, 4,096 memory cells are swapped in and out for each row repair, when repair using redundancy elements is performed. Note that while only 1 out of the 32 local wordlines might actually be defective, all the local wordlines must be swapped in and out. Thus, this solution offers only very coarse granularity with regard to the replacement of defective elements of a memory device.
Thus, there exists a current need in the art to be able to replace defective elements of an integrated circuit memory device, such as defective local wordlines of a SRAM, with redundant elements in a manner which does not require replacement of all like elements of the memory device.